The work proposed for the next year will be a continuation of that done in the preceeding five or six years, namely, investigations of mechanisms by which various added solutes and changes in physical conditions modulate radiation sensitivity of the inert bacterial spore. A large number of added chemicals will be used to investigate in particular the modifications that are necessary in the hydroxyl radical theory of radiation sensitivity that has been developed in this laboratory over the past several years. These include the addition of many metals as well as certain organic materials. The end points will be changed slightly to include radiation mutagenesis and to include also investigation of strains of Bacillus megaterium whose spores differ in basic radiation sensitivity. Emphasis will be placed on recognition of the relationships of the added sensitizers to the bacterial spore, including the measurement of the uptake of the metals by the spores as well as the kinds of complexing that the metals accomplish within the spore.